The present invention relates to a method for producing a support for electrophotographic material or for electrostatic recording material which is light in weight and excellent in solvent resistance and electroconductivity.
Main characteristics with a support for electrophotographic material or for electrostatic recording material (this is referred to as a base paper hereinafter) should possess are as follows:
1. It must be excellent in solvent resistance. PA1 2. It must have a good electroconductivity. PA1 3. It must not have adverse effect on electrophotographic layer or electrostatic recording layer.
The property of the above (1) is required for preventing permeation of solvent into a base paper to make the coated film homogeneous because organic solvents such as toluene, xylene, etc., are often used for coating of a recording layer. The property of the above (2) is required for sufficient charging and discharging of a recording layer to obtain excellent image.
In order to obtain the above properties (1) and (2), conventionally, natural or artificial viscous adhesives have been used as a permeation preventing agent and one or more of inorganic salts and polyhydric alcohols such as sodium chloride, calcium chloride, iron chloride, etc., and ethylene glycol, glycerine, sorbitol, etc., have been used as an electroconducting agent (See Japanese Pat. No. 29316/64). However, according to such method, there have been such defects as a high dependency of electroconductivity on humidity, low preservability of recording paper caused by use of inorganic salts, etc. There have been proposed a method for improving electroconductivity and preservability by combination of a cationic antistatic agent comprising a quaternary ammonium salt of a polymer and an anionic active agent having hydrophilic group (Japanese Pat. No. 19195/69). However, according to said method, although electroconductivity and preservability can be improved, solvent resistance is not improved. For imparting both electroconductivity and solvent resistance, there has been a method which comprises impregnating or coating paper with an aqueous solution of a mixture of a highly saponified styrene/maleic anhydride copolymer of high polymerization degree and a highly saponified styrene/maleic anhydride copolymer of low polymerization degree or said mixture to which a natural or synthetic sizing agent is added (see Japanese Pat. No. 13166/71). However, according to this method, there is the possibility of quality of image lowering due to shortage in electroconductivity at low humidity in both cases of using only styrene/maleic anhydride copolymers different in polymerization degree and saponification degree and using said copolymers to which glue-like silica, fine grain silica and water soluble polyethylene glycol are added.
Therefore, in order to safisfy said requirements for base paper by these conventionally proposed methods, it has been necessary to apply the treating materials in a considerably large amount to a support.